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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Iterable container as generic parameter
Date: Thu, 25 Jan 2018 22:50:50 -0600
Organization: JSA Research & Innovation
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Xref: reader02.eternal-september.org comp.lang.ada:50158
Date: 2018-01-25T22:50:50-06:00
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"Lionel Draghi" <lionel.draghi@gmail.com> wrote in message 
news:6427a793-91a4-4feb-b067-ed89b4c04421@googlegroups.com...
>> As to the question you didn't ask, you clearly need the container type
>> somewhere in your interface, so you can pass container objects. (Or, I
>> suppose, you could reference the type used in the instance of the
>> Iterator_Interfaces.) Otherwise, you just have methods but no data. And
>> there isn't anything interesting that you can do with just methods!
>
>Thanks Randy for the answer, this is actually my question.
>And what you put into parenthesis was what I was trying to do.

Formal package parameters that are given by <> are available inside the 
generic unit given their formal names.

But now looking at the definition, I see the container type isn't in that 
signature.

>Here is my point :
>If I limit the procedure scope to a specific container, the generic is 
>simple :
...
>But if want something that could be used with both Lists and Maps, I have 
>to provide much more parameters :

...

Emmanuel already described using signature packages for this.

But I probably would just use your original spec and add the container type 
and iterator function, something like:

generic
   type Cursor is (<>);
   with function Image (C : Cursor) return String;
   type Container (<>) is private;
   with package Iterator_Interfaces is
     new Ada.Iterator_Interfaces (Cursor, others => <>);
   with function Iterator (C : Container) return 
Iterator_Interfaces.Forward_Iterator'Class;
function List_Image return String;

Not sure if this is enough (I have work to do tonight!), but this is where 
I'd start.

                              Randy.